CALCULATE YOUR RATE
A cyclist can shed two to three pounds an hour while riding hard. Each pound equals about 16 ounces of sweat. But the human body can’t replace all of the fluid it loses, so aim to drink seven to 10 ounces every 10 to 20 minutes, depending on your hourly sweat rate. Use this calculator to determine your sweat rate.

HOW IT WORKS
Sweat is like central AC for your body. On hot days or as you’re grinding up a hill, glands under the skin produce sweat and send it to the surface, where it evaporates. Each drop that turns to vapor pulls heat away from your body, and you feel cooler. The hotter you get, the more you sweat.

WHEN IT DOESN’T WORK
On days when there’s a lot of moisture in the air, sweat can’t evaporate­ as quickly, making it harder for your body to cool off. This is why heat-related­ problems like cramps, exhaustion, and heatstroke are more common in humid environments than in dry ones.

STINKS
Your diet may be to blame. Caffeine stimulates sweat glands under your arms and in your scalp and groin, which secrete a fatty, odiferous sweat. And if you eat a very low-carb diet, your body breaks down protein and fats, creating acetone, which is excreted through sweat and has a distinctive ammonia smell.

POURS
You’re hydrated and working hard. Seasoned riders may not sweat more than cyclists who aren’t as fit; but they’re able to work harder and produce more sweat. In hot conditions, however, fitter athletes have greater sweating capacity, according to research published in The American Journal of Physiology.

STAINS
You may be losing a lot of salt. Less-fit riders who aren’t used to riding in heat shed more sodium than their fitter, heat-acclimatized counterparts. Choose a drink with 400 to 600mg of sodium per serving.

STOPS
"You’re not adequately replacing your fluid loss," says Penn State University sweat researcher Caroline Smith, PhD. Performance starts to plummet when you lose more than 2 percent of your body weight. This is a sign of heat exhaustion, when your core temperature can rise quickly, potentially leading to heatstroke.